This invention relates, in general, to microwave oscillators, and more specifically, to optical injection locking of microwave oscillators.
Recent developments in microwave oscillators incorporate modulated light sources to stabilize the oscillator frequencies. When the modulated frequency of such light sources approximates the free running oscillator frequency, injection locking occurs and the oscillator produces a clean output signal at the injected modulated light frequency. However, when the free running oscillator frequency is substantially different than the injected modulated light frequency, injection locking does not occur. Previous injection locking schemes have been limited to low tuning ranges. One such scheme reported a 12 MHz locking range for a 10.779 GHz oscillator. "Phase and Frequency Coherency of Multiple Optically Synchronized 20 GHz FET Oscillators for Satellite Communications", IEEE Microwave Theory and Techn. Symposium Digest, 1987, pp. 823-826. The scheme used a PIN diode to detect the modulating light signal and electrically lock the oscillator.